I would gave bought a Grainger for my HB JB build, but the string spacing was wrong for me. But I did get my Hipshot bridge from BTN. A lot of my Hipshot kit has come from them. Always had good service and when I got a duff tuner with a very stiff section, they immediately just sent me a replacement without having to send the original back, which arrived the next day.
I must say that the Grainger certainly looks machined whilst the Sung Il looks cast. One may have certainly inspired the other.
I can attest that the Sung Il is cast. The Grainger website says it's milled on a CNC machine. It looks like about as good an option as I have seen in an alu locking bridge, and certainly competitively priced with the Hipshot...which is the only other alu locking bridge I can think of. Of course, I haven't seen one for sale by a US seller, which undercuts price-competitiveness for me at least....
Not my first Sung Il bridge...but the latest, and it has a bit of an oddity. I have used three bass bridges from Sung Il and all have been quite good and very well finished. Two are BB404's for F style bases and one BB100 for a G style bass.
I just got my 4th, a gold G style roller bridge:
It is really well finished...first time I have gotten one in gold (in spite of how the pics p1 of this thread look). The oddity is that the eBay page where I got it, and the base of the bridge says it's a BM003. It's actually a BM005. If you look on the Sung Il website, a BM003 is not a roller saddle bridge, but the BM005 is.
I suspect that the reason is that the base on both bridges is identical. The only actual difference is the saddle--so Sung Il doesn't bother to create a separate cast for the BM005 bridges. In any case the bridge looks and feels great.